Radio receiving system



P. o, FARNHAMA- RADIO RECEIVING SYSTEM July 18, 1933.

Filed Nov. 4, 1932` FIB. l.

Patented July 18, 1933 UNITED STATESv PATENT o1=1=1caw PAUL O. FARNHAM, OF BOONTON, NEW JERSEY, .ASSIGNOR T0 RAIQIO FREQUENCY LABORATORIES, INCORPORATED, OF BOONTON, NEW JERSEY, 4A CORPORATION 0F NEW JERSEY RADIO RECEIVING SYSTEM .Application led November 4, 1932. Serial No. 641,278.

This invention relates to radio receiving systems of the automatic gain control type, and particularly to methods of and circuit arrangements for suppressing all output from the receiver when the amplitude of the carrier wave to which the system is tuned falls below a predetermined value..v

Various methods and circuit arrangements for accomplishing this general result are described and claimed in my copending applications Ser. No. 524,388, filed March 21, 1931, Ser. No. 585,593, filed January 8, 1932, and Ser. No. 603,849, led April 7, 1932. As explained in those applications, itis highly desirable to suppress intercarrier noise in receivers, particularly those equipped with automatic gain control. It will here be suiiicient to recall the fact that the sensitivity of a high .gain receiver employing the commonly used automatic gain control system becomes so great, when the system is tuned to a frequency at 'which only aweak carrier wave or none at all is received,vthat the amplified 'receiver noise rises to levels that argl quite intolerable at the'loud speaker output.

Objects of the present invention are to provide, in a radio receiverv system, .improved methods of and circuit larrangements for automatically eliminating this noise output, and in fact all outputwhen the amplitude of the carrier wave to which the receiver systeznis tuned fallsy below a given value, ri. e.,"below the noise level.

Further objects are to provide methods and circuit arrangements for obtaining the statedl results with a minimum of circuit elements and tubes. More particularly, objects are'to provide radio receiver systems of thenoise suppression type, and which are characterized by the employment of a vacuum tube of new design and associated circuit elements for effecting the noise suppression action by circuits that perform the function of automatic gain control, the tube being of the multiple element type and including elements for vdiode rectification and for amplification. l

These and other objects and advantages of the invention will be apparentfrom the following specification when taken with the accompanying drawing, in which:

systems embodypress1on in conjunction with the operations -of detection and automatic gain control, but.

does not include any adjustment for controlling the relative carrier levels required for noise suppression and for automatic gain control.

In the drawing, the reference character A identifies a radio amplifier, including one or more vacuum tubes, which receives carrier wave energy from an appropriate -collector structure, and which works into a detector and audio amplifier or other load circuit. The exact design and construction of these elements are not a part of the invention and any desired type of tuned radio frequency or superheterodyne amplifier may be employed.

The output coil l of the last tube of the amplifier A applies the amplified radio voltage, which will be of intermediate frequency in the case of a superheterodyne amplifier, to the tuned input circuit composed of the coils 2, 3, the fixed condenser 4 and the tuning condenser 5. The fixed condenser serves as a blocking condenser for direct current and is large in comparison to the tuning condenser.

The radio voltages developed across the coils of the input system -are applied to the separate' anodes of a tube 6 of the type lmown commerciallyas type and which include' a cathode K, anodes A1 and Az which cooperate with cathode K to form two diode reci tiiers, and a/grid G and plate P which cooperate with the cathode to form a triode am-l plier. The inner terminals ofv 1. e., those connected to the blocking Aconcoils 2 and 3, 9o.

denser 4 have substantially the same radiof1-":`

voltage, and, for convenience of description,

the outer- 'terminals of coils 2, 3 will be 1.

terned thehigh potential terminals of those co1 s. v

The high potential terminal of coil 2 is connected to the anode A1, and the inner or low potential terminal is connected directl but for radio voltages only, to the catho e K by the condenser 7. For direct current,

j tem.

yThe voutput circuit of the triode elements of tube 6 is shown as a transformer 11 which has its primary connected between plate P and a source, indicated as -l-B, of direct current potential.

- The outer or highA potentialv terminal of the input coil 3 is connected to the anode A2 resistances constitute a voltage divider which.

vvoltage across coil 3 and the innerlterminal of the coil is connected to ground through the resistance 12. The cathode K is connected to ground (through resistances as will Abe described hereinafter) and therefore thev described circuit elements constitute a diode rectifier, the -direct current voltage developvedacross resistance 12 being applied, through a filter comprising a resistance 13 and condenserv 14, and a lead 15, to the amplifier A as a gaincontrol bias.

The cathode K is connected to the source +B of direct current-potential through a resistance 16, and is connected to ground through the. series resistances 17, 18. These places the cathode K at a fixed positive potential with respect to anode A2thereby preventing the development' of a rectified or gain control voltageeXceeds the negative bias on the anode A2. This is highly desirable in automatic gain control systems as it avoids loss of sensitivity for received carrier voltages vbelow that level which, at maximum gain, will develop the normal output of the system.

As the two diode rectifiers work upon alternate halves of the amplified wave, this delay action of the gain control vrectifier has substantially no e'ect upon the wave impressed upon the detector. This method and circuit arrangement for avoiding distortion is described and claimed in my application Ser. No. 611,402, filed May 14, 1932.

A direct current amplifier tube 19, of the screen grid type, and its associated circuit elements serve as the means for suppressing all receiver output fior received `carrier waves of less than a predetermined-amplitude. The control grid G1 of the tubet19 is connected by lead 20 to the output terminal of the resistance 13 of the'filter system of the gain control rectifier. The screen grid G2 is connected by resistance 21 to the junction of resistances 1 3 18 in the cathode circuit of tube 6, and through resistance22 tothe control grid G of the triode amplifier'elements of tube 6.

untilthe peak radio current flows in the plate and screen grid ciry cuits. Current fiow in the plate circuit of tube 19 produces a voltage drop across resistance 8 which places the cathode K at a positive potential with respect to the detector anode A1. Similarly, current flow in the screen grid circuit increases the1 negative bias on grid G of tube 6 above that value which is determined by the voltage drop across the cathode resistance 17. Under these conditions a relatively low value of` modulated radio voltage across coil 2`will not produce an audio frequency voltage across resistance 8 as a high negative bias is impressed upon the detector anode A1 and, if

an audio voltage is developed across resistance 8, it will not be amplified by the triode elements of tube 6 since the grid G is subj ected to a high negative bias.

When the received carrier energy rises above lthe noise level, the diode rectifier formed by. anode A2 and cathode Kcomes into action, i. e., when the peak ra'dio voltage across coil 3 exceeds thev negative bias due to the voltage drop across resistances 17 18. When a direct current voltage is develo ed across resistance 12, a negative potentia is applied to the control grid G1 of tube` 19 and the space current flow in that tube is reduced or cut off. When this occurs, the reduction vorsuppression of plate current flow throu l1 resistance 8 removes the negative bias on trifle detector elements A1, K, and an audio frequency voltagey is thereby developed across resistance 8. Simultaneously, the reduction or suppression of current fiow in the screen grid circuit-of tube 19 reduces the negative bias on grid Gof the triode, and the audio voltage impressed on grid G is amplified in the plate circuit. So long as the received carrier energy is below that value which results in rectification by the gain control rectifier A2, K. all audio output is suppressed by the blocking of the detector and the audio amplifier. As the received carrier energy rises above the critical value, the blocking bias voltages and audio amplifier elements of tube 6 and the receiver system functions in the usual 'i manner as an automatic gain control receiver for holding the audio output substantially independent of variations in received carrier energy. In other words, all audio output is suppressed when the received energy 1s below a predetermined critical value and, whenthe received energy is of sufficient magnitude to produce a proper audio signal, all bias voltages which effectthe noise suppresare removed from the detector Y the remaining electrodesv of v1, and the inputy sion are removed and the normal amplifier and detector action takes place.

Suitable values of some of the circuit elements and energizing potentials are Resistor 8=l00,000 ohms.

Resistor.12= 1 megohm.

Resistor 13:0.5 megohm.

Resistor 16=11,000 ohms.

Resistor l7=560 ohms.l

Resistor 18:1,250 ohms.

Resistor 21=100,000 ohms.

Resistor 22=1 megohm.

Condenser 4= .01 .microfarads Condenser 7 =100 micromicrofarads.

Condenser 9=.01 microfarads.

Condenser 14=.05 microfarads.

+B lead=200 volts positive to B.

In the operation of the circuit shown in Fig. 1, there is no provision for any adjustment of the critical voltage level at which the automatic gain control cornes into action and the Vnoise suppression bias voltages are removed; The circuit shown in Fig'. 2 includes adjustable circuit elements for independently adjusting the critical input levels of the noise suppression system and the auto` matic gain control.

An independent diode for automatic vol? urne control is provided in the Fig. 2 circuit by an extra anode A1 in the last tube 23 of the radio frequency amplifier A; the extra anode operating with the common cathode but being located outside of the range of infiuence of a conventional screen grid amplifier tube.

The inpt'or coupling coil 24 is connected to the control grid G1 and to the cathode K through the bias'resistor 25 which isshunted by a condenser 26. A resistor 27 is connected between resistor 25 and ground to place the cathode K at a more positive potential than that ofthe anode A1 which is connected to ground through the direct current output resistance 12. The amplified radio frequency voltage developed by the amplifier elements of the`tube 23 is impressed upon this diode rectifier through the condenser 2 8 which is connected to .the anode A1 and to the tuned output circuit 29 of the amplifier. When the received radio frequency voltage rises abovel the critical value determined by the potential drop across the series resistors 25, 27, rectification takes resistor 12" is applied to'the control grids of the preceding tubes through the filter formed by resistance 13 and condenser 14:. The multiple function detector stage tube 6 is of the same 55 type as that shown in Fig. circuit 30 is connected be#-4 tween the anode A1 and, foralternating current only, directly to the cathode K through the radio frequency by-pass condenser 3l. For direct current, the low potential terminal of the input circuit 3Q is connected to the plate P of the direct current amplifier 19.

place and the voltage across 6 through the blocking condenser 9 and the adjustable tap '10 which provides a manual control of the audio output level. The noise suppression diode rectifier has its anode A2 .connected to the input circuit 30 through the blocking condenser 32 and the direct current output resistance 33 of this diode is connected by an adjustable tap 34 to the series resistances 17 1'8 in the cathode circuit. The adjustable'tap 34 permitsa control of the negative bias on anode A2 and the adjustment of this tap determines the critical radio frequency Ivoltage below which the detector and audio amplifier are rendered inoperative by the action of the tube 19.

1 The control grid G1 of the tube 19 is connected to anode A2 by resistance 35 and to the cathode K through an audio fre-A quency condenser 36. As in the Fig. 1 circuit, the screen grid G2 is connected to the junction of resistances 17 18 by a resistance 21', and isschnected. to the control grid G of the tube 6. The cathode K of tube 6 is connected through a resistance 16L-to a point of ositive potential +1 B, and the plate circuit ofp tube 6- includes the primary of an audio frequency transformer 11 and theI plate current source -I- B. In general, operation of this circuit will be apparent from'the deseriptionof the Fig.- l circuit. By means of the adjustable tap 34, the audio output from tube 6 may be cut off for radio frequency levels below lany predetermined limit, which limit is preferably leo les

ceiver to meet the particular noise interference 4conditions at the locality in which the receiver is to be operated.

A separate adjustment of the critical volt- Vage` at which the automatic volume control becomes operative may be had by making the resistor 27 adjustable but, in general, this 'Y regulation is neither necessary nor desirable, A since the operating characteristics lof the automatic volume control are determined by the receiver design and not by conditions peculiar to any one locality. I

I claim:

1. In a radio receiver, the combination of a multiple function tube having therein the elements of an amplifier and two rectifiers, input circuit elements for impressing radio frequency voltages upon both rectifiers, an audio frequency output circuit for one rectifier, means coupling the input circuit of the amplifier to said audio frequency output circuit, a direct current output circuit for the second rectifier, and means energized by the rectified voltage developed in said directeurrent output circuit for controlling the operation of said first rectifier.

2. In a radio receiver, the combination of a multiple functionltube having therein the elements of an amplifier and two rectifiers, input circuit elements for impressing radio frequency voltages upon both rectifiers, an audio frequency output circuit for one rectifier, means coupling the input circuit of the amplifier to said audio frequency output circuit, a direct current output circuit for the second rectifier, and means energized by the rectified voltage developed in said direct current output circuit for controlling the operation of said amplifier.

3. In a radio receiver, the combination of a multiple function tube having therein the elements of an amplifier and two rectifiers, input circuit elements for impressing radio frequency voltages upon both rectifiers, an

' audio frequency output circuit for one rectifier, means coupling the input circuit of the amplifier to s'aid audio frequency output circuit,a direct current output circuit for the second rectifier, and means energized bythe rectified voltage developed in said direct current output circuit for suppressing substantially all output from said amplifier when the impressed carrier voltage falls below a predetermined value. j

4. In a radio receiver, the combination with a tube having two anodes, a control grid, plate and cathode, of input circuit elements for impressing radio frequency voltages between eachvanode and the cathode, circuit elements cooperating with one anode and the cathode to form the output circuit of a diode detector, an input connection fromthe control grid to said'output circuit, an audio frequency load in circuit with said plate and cathode, a direct current output circuit for the diode formedby said cathode'and second anode, and means actuated by the direct current voltage developedin said direct current output circuit for controlling the operation of said 4detector diode.

5. In a radio receiver, the combination with a tube having two anodes, a control grid, plate and cathode, of input circuit elements for impressing radio frequency voltages between each anode and the cathode, circuit elements cooperating with one anode and the cathode to yform the output circuit of a diode.

detector, an input connection from the control grid to said output circuit, an audio frequency load in circuit with said plate and cathode, a direct current output circuit for the diode formed by said cathode and second anode, and means actuated by the direct current voltage developed in said direct current output circuit for controlling theoperation of the audio frequency amplifier formed by said cathode, control grid and plate.

6.' In a. radio receiver, the combination with a tube having two anodes, a control grid,

plate and cathode, of input vcircuit elements for impressing radio frequency voltages Abetween each anodeand the cathode, circuit ele.

' output circuit for controlling the bias voltage impressed upon said detectordiode.

7. In a radio receiver, the combination with a tube having two anodes, a control grid, vplate and cathode, of input circuit elements for impressing radio frequency voltages between each anode and the cathode, cir- -cuit elements cooperating with one anode and the cathode to form the output circuit of a diode detector, an input connection from the control grid to said output circuit, an audio frequency load in circuit with said plate and cathode, a direct current output circuit for the diode formed by said cathode and second anode, and means actuated by the direct current voltage developed in said direct current output circuit for controlling the bias voltage impressed upon the audio frequency amplifier formed by said cathode, control grid and plate.

8. In a radio'receiver, the combination with a tube having two anodes, a control grid, plateand catho-de, of input circuit elements for impressing radio frequency voltages between each anode and the cathode, circuit elements cooperating with one anode. and the cathode to form the output circuit. of a diode detector, an input connect-ion from the y for the diode formed by said cathode and sec- H ond anode, means impressing bias voltages upon said diode detector and upon said ampliiier to render the same inoperative, and y s means including said second rectifier for automatically removing said bias voltages when the received radio frequency voltage exceeds a predetermined value.

-9. The invention as setforthin claim 8, wherein said last means includes an ampli fiertube for amplifying direct current volt.- ages developed by the rectifieraction of said cathode and second, anode.

' v10. The 'invention as set forth in claim 8, wherein said last means includes a screen grid amplifientube for amplifying direct cur- -rent voltages vdeveloped by the rectifier action vof said cathode and second anode, the screen grid and plate circuits of said screen grid amplifier tube includingv resistances which are connected between'said cathode s in lcombination with means impressing upon ers Y a'rectiiied current.

trol gri of said irsttube. v

11.111 a radio` receiver, the combination with a'radio frequency inputcircuit, an audio 5 fiequencyroutput-circuit, of a multiple function tube housing the'elementsof two diode rectifiersand an amplifier, said rectifiers .be`

- ing coupled to said input circuit, van audiofrequency output circuit for' one rectifier, ad-l m5"j'ustable meansforim-pressin upon the'said' the audio fre- `quency voltage developed inthe'v output cir. cuit of said first-rectifier, a .direct current,l output circuit forsaid second rectifier, and.

- amplilierfal desired portion o 5 means energized by the rectified output of Y said secondy rectifier` for :controlling the -flow` of alternating current in one of kv saidaudiefrequency output circuits.

. 12'. The inventionas set-forthiiiclaimi11', *0f in .combination with meansv foriin ressing on one off:saidrectif iei"s"a=-biasf. vo tagey VtoV Y render the' 'saineA inoperativezforzradio frequency voltagesbelow'aipmdetermined criti- V(BIIJV lle; 13. The invention asset forth in claim 11,

each rectifier a'bias voltage which ren the same-,inoperativefor radiofrequency voltages-below predetermined critical values,

'30 and" wherein the said means energized by thel` ,rectified output of jthesecond rectifier removes-the bias voltage from said first rectilier when *the radio frequency voltage rises above the predetermined value at which said al""second rectifier becomes pera'tive 'to pass 14. In a radio receiver, the combination gwith a tube having an anode, a control grid,

plate and cathode, 40 pliier, means cooperating with said anode and cathode to form a diode detector work- .ing out of saidamplifier, means for automatically controlling the gain of said radio frequency amplifier, circuit elements for impressing upon said control grid an'audio frequency voltage developed b said Idiode etectoi', an audio frequency loa in the plate circuit of vsaid vtube,- means establishing a `bias voltage between cathode and another tube element to suppress the transmission of audio frequency currents by said tube, and meansaoperable automatica ly when the received radio frequency volta e rises aboveI .a critical level to reduce the ias voltage to permit normal transmission by said tube.

' The invention as set forth in claim 14,

"and, respectively, the iirst anode and-the cona second 'anode withinsaid tube' and coo o uency. amplifier, and; means yindepe' ifi'deiit ol -said of aradio frequency amwherein said-biasreduc` ineani'iincludes` said means for automatic they gain of said amplifier.

16;` The .invention'as set f orth'iiil v j 'l whereinfsaid means for automatically fcon- 179m trolling-the in of said'amleier includes a ondlano e within said'tu and coopera t g with said cathode'to .form a diode recer., l 17;;-Tlie invention as set forth-in claim 14,* wherein-said means foi-automatically controllingthe gainof said amplifier includes erating. withsaid cathodeV to form a-di e rectifier, anidfsaid bias reducin VAmeans in'- cludes adirect vcurrent amp er jworgng out.ofsaiddiode.rectiiier. f 18. `Iii-'aradio receiver, a radio l amplieig'ja multiple.; function' tube -incl'u amplifier, circuit velements 188,1

vdetector 4-between saidra'dio frequency aincontrolling the gain offsai l diode rectifier for reducing the said inlpressed bias voltage when the radio frequency voltage on said detector exceeds the predetermined value. l

20. The'combinati'on with a multi le funcv tion tube housing the elements of a 'ode detector, a `diode rectier, and an amplifier, of circuit 'elements formin a. radio frequency input circuit for said detector and 110` rectifier, circuit elements icoupling said amplifiei` to the audio freqiency output'circuit of said vdetector means iasin -said detector and .said ampliiierto render t 'e same inoperative, and means energized by the rectified 116 output of said rectifier when the radio frequenc voltage impressed thereon exceeds a pre etermined value for removing the bias voltages which render the detector and amplifier inoperative. Y, izo PAUL l ing a dioderd'etectong and.audio frequenc Ilv DISCLAIMER 1,919,160.Pault0. Farnham, Boonton, N. J. Ramo RECEIVING SYSTEM.. Patent dated July 18, 1933. IDisclaimer filed October 25, 1935 by theassignee, Radio Uorport'ionof America.

H ereby enters this disclaimer to the said "claims of said Letters Patent which are in the following Words, to Wit:

14. In a radio receiver, the combination with a tube Shaving an anode, a controll grid,.plate and cathode, ofa radio frequency amplifier, means cooperating `with said anode and cathode to form a diode detector vvorking out of said amplier, means for automatically controlling the gain of said radio-frequency amplifier, circuit elements for impressing upon said cont-rol grid anv audio fre uency. voltage developed by said l diodedetector, an audio frequency load in thep ate'oircuit of said tube, means establishing a. bias voltage between cathode'and another tube element to suppress the transmission of audio frequency currents by said tube, and means operable automatically when the received radio frequency voltage rises-:above a critical level to reduce the bias voltage to permit normal transmission by said tube. Y

16. The invention as set forth in claim 14, wherein said means for automatically controlling. the gain of said amplifier includes a second anode Within said tube and cooperating with said cathodeto' form a diode rectifier. [O cz'al vGazetta November 1 .9,- "1 .935 .l 

